1 | P a g e

Alcohols are the hydroxyl derivatives of aliphatic hydrocarbon in which the –OH group

is attached to alkyl group.

R-H → R-OH

CH4 → CH3OH

(Methanol)

C2H6 → C2H5OH

(Ethanol)

The aromatic hydroxyl compounds in which one or more hydroxyl groups are directly

attached the aromatic nucleus (i.e. benzene like ring) are called Phenols.

Ph -H → Ph-OH The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group

(R–O/Ar–O) yields another class of compounds known as ‘ethers’, for example,

CH3OCH3 (dimethyl ether). ethers as compounds formed by substituting the hydrogen

atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group.

+OR

R-H → R-O-R

Nomenclature of Alcohols The general formula of monohydric alcohols is CnH2n+1OH where n=1, 2, 3……….etc..

or R-OH where R is any alkyl group .These are named by the following systems.

(i) common system: In the common system, monohydric alcohols are called alkyl

alcohols their names are derived by adding the word alcohol to the name of the alkyl

group present in the molecule.

(ii) carbinol system: In this system, methyl alcohol (CH3OH) is called carbinol while

other alcohols are named as alkyl or aryl derivatives of carbinol.

(iii) IUPAC system: Alcohols are named by replacing ‘e’ in the name of parent alkane

by ‘ol’. The IUPAC and common names for several alcohols are given below

Structure Common IUPAC

CH3OH methyl alcohol Methanol

CH3CH2OH

CH3CH2CH2OH

ethyl alcohol

n-propyl alcohol

Ethanol

Propan-1-ol

l

Alcohols are organic compounds that have one or more hydroxy (-OH) groups bonded to

the carbon atoms in aliphatic compounds. They occur widely in nature and have many

industrial and pharmaceutical applications. For example, methanol and ethanol are two

industrially important alcohols.

2 | P a g e

Alcohols and Hydrogen Bonding The differences in physical properties between

alcohols and alkanes-

1. Alcohols have higher boiling points

than alkanes of similar molecular mass.

2. Alcohols have much higher solubility in water

than alkanes of similar molecular mass.

Figure shows the association of ethanol molecules in

the liquid state (only two of the three possible

hydrogen bonds to the upper oxygen are shown here).

Alcohols have higher boiling points and are more soluble in water than hydrocarbons.

STRUCTURE

In alcohols, oxygen atoms are sp3 hybridized. Two of the four sp3 hybridized orbitals of

oxygen get involved in formation of σ-bond with hydrogen and carbon respectively In

alcohols, both carbon and where as rest of two sp3 hybridized orbitals contain lone pair of

electrons. C-O–H bond angle is found to be as 105o ( rather than normal tetrahedral

angle 109.5O) Deviation from normal angle can be explained on the basis of greater

repulsion by lone pairs than bond pairs.

CLASSIFICATION OF ALCOHOLS

On the basis of number of hydroxyl groups present in a molecule, alcohols are classified

as

(I) Monohydric alcohols : contain only one hydroxyl group in their molecules.

CH3 OH : methyl alcohol (CH3)3C- OH : Tert. butyl alcohol

(II) Dihydric alcohol

contain two hydroxyl groups situated on different carbon atoms.it is also called diols or glycols

(iii) Trihydric alcohol

Compounds in which three hydrogen atoms are replaced by three hydroxyl groups.

Among the compounds with carbon-oxygen single bond are the classes ofalcohols, phenols and

ethers having the following general structures.

3 | P a g e

CLASSIFICATION OF MONOHYDRIC ALCOHOLS

Monohydric alcohols are classified according to the type of hybridization of the carban

atom to which the hydroxyl group is attached.

1. Compound containing C sp3 – OH bond.

In these alcohols, the –OH group is attached to an sp3 –hybridized carbon atom

of an alkyl group. (i) Primary alcohol(1

o): In these alcohols, the hydroxyl group is attached with

primary (1o) carbon atom. The general formula is R-CH2-OH. R may be H or alkyl group (ii) Secondary alcohol (2o): In these alcohol attached with secondary (2o) carbon atom. The general formula is

R and R’ may be same or different

(iii) Tertiary alcohol(3o): In these alcohols, the hydroxyl group is attached with, tertiary (3o) carbon atom. General formula is

R, R’, R” may be same or different

iv) Allylic alcohol : In these alcohol, the –OH group is attached to an sp3 hybridized

carbon next to the carbon-carbon double bond. i.e. to an allylic carbon

(v)Benzylic alcohols: In these alcohols, the –OH group is attached to a sp3- hybridized

carbon atom next to an aromatic ring. It may be 10, 20 and 30.

4 | P a g e

2. Compound containing C sp2

-OH bond

In these alcohols, the –OH group is attached to a carbon atom of double bond i.e. vinylic carbon. These are also called vinylic alcohol.

CH2 = CH2 – OH (vinyl alcohol, unstable)

ISOMERISM IN ALCOHOLS

1. Chain isomerism : Alcohols containing four or more carbon atoms

exhibit chain isomerism in which the isomers differ in the chain of carbon atoms

attached to the hydroxyl group Molecular formula C4H9OH shows the following

isomers.

CH3 = CH2 – CH2 – CH2 – OH CH3-CH-CH2CH3

( Butan – 1 –ol) OH (Sec-Butyl alcohol)

CH3

CH3- C- OH

CH3 (tert-butyl alcohol)

2.Position isomerism : Alcohols containing three or more carbon atoms show

position isomerism in which the isomers differ in the position of hydroxyl group when

carbon chain is the same. 3.Functional group isomerism: Saturated monohydric alcohols containing two or more carbon atom show functional isomerism with ethers e.g.

CH3 – CH2 – OH (ethanol ) and CH3 – O – CH3 ( methoxymethane) Besides the structural isomerism, alcohols having asymmetric carbon atom exhibit optical isomerism e.g.

GENERAL METHODS OF PREPARATION OF ALCOHOLS

1. Hydrolysis of alkyl halide:

Alkyl halides on heating with dilute aqueous alkali give corresponding alcohols. Better

yields are obtained when alkyl halides are heated with moist silver oxide.

∆ R-X + KOH (aq) → R-OH + KX

(moist) Ag2O

R-X + AgOH → R-OH + AgX ∆

5 | P a g e

This method is not satisfactory for preparing alcohol because haloalkanes are

themselves obtained from alcohols and in higher halides, the alkenes are formed as side

products However, satisfactory results are obtained by using moist silver oxides (AgOH)

(A) Primary (10) alkyl halides gives good yield of alcohols, while tertiary butyl

halides mainly give alkenes due to dehydrohalogenation

(B) Secondary(2o) alkylhalides gives a mixture of alcohol and alkene

Br OH ∆ CH3-CH-CH3 +KOH → CH3-CH-CH3 + CH2-CH=CH2

hydrolysis of 1o halides proceeds by SN2 mechanism while those of 3o halides by SN1

mechanism. The hydrolysis 2o alkyl halides may proceed by SN1 or SN2 mechanism

(2) Hydration of alkene :

The term hydration means addition of a molecule of water. The hydration of alkenes can

be carried out either indirectly or directly. In the indirect process, alkenes are passed

through con. H2SO4 to form alkyl hydrogen sulphates, These upon hydrolysis with

boiling water give alcohols. thus 1.Direct hydration

∆

CH2=CH2 + H2SO4 → CH3–CH2–OSO3H+H2O → CH3CH2OH + H2SO4 Ethene ethyl hydrogen sulphate Ehanol

HOH/∆

CH3-CH=CH2 + H-OSO3H → CH3-CH-CH3 → CH3-CH-CH3 + H2SO4 Propene OSO3H OH isopropyl hydrogen sulphate Propan-2-ol

Mechanism:

The mechanism of acid catalysed addition of water (hydration) to alkenes involves following stapes: Step I : Electrophilic attack by hydronium ion (H3O+) on alkene gives an intermediate carbocation

H2SO4 → H+ + HSO4

-

6 | P a g e

Step II: Nucleophilic attack by water on carbocation to yield protonated alcohol

Step III: Deprotonation ( loss of proton) to form an alcohol

Addition of H2SO4 follows Markownikoff’s rule

2.Indirect hydration

a) Oxymercuration - demercuration : Alkenens react with mercuric acetate

(CH3COO)2Hg or Hg(OAc)2, to form oxymercuration products which upon reduction

with NaBH4 in basic medium give demercuration product alcohols. thus,

Step-1:Oxymercuration

Step-2:Demercuration

7 | P a g e

b) Hydroboration–Oxidation: Diborane (B2H6) is an electron deficient molecule

.Therefore, it acts as an electrophile and reacts with alkenes to form trialkylboranes

which upon subsequent oxidation with alkaline H2O2 give alcohols. Thus

Ether

R-CH=CH2 + B2H6 → RCH2-CH2-BH2

RCH2-CH2-BH2 + R-CH=CH2 → (RCH2CH2)2BH

(RCH2CH2)2BH + R-CH=CH2 → (RCH2CH2)3B

H2O2/OH-

(RCH2CH2)3B → 3RCH2-CH2-OH + H3BO3

Reaction ultimately results in anti Markownikoff’s addition of water

(3)Hydrolysis of esters :

H+ or OH-

RCOOR’ +H2O → RCOOH + R’OH

(4)Hydrolysis of ethers:

H2SO4

R-O-R’ + H-O-H → R-OH + R’-OH

(5)Action of nitrous acid (HONO) on primary amine:

Aliphatic primary amines on treatment with nitrous acid (NaNO2+HCl) give primary

alcohols.

RNH2 + HONO → R-OH + N2↑ + H2O

Or

Methylamine does not yield methyl alcohol only, but in excess of nitrous acid the other

products may be formed as, methyl nitrite or dimethyl ether.

CH3NH2 + 2HNO3 → CH3 – O – N = O + 2H2O + N2↑ Methyl nitrite

2CH3NH2 + 2HNO3 → CH3 – O – CH3 + 2H2O + N2↑

Dimethyl ether

8 | P a g e

(6)Reduction of aldehydes and ketones:

Aldehyde and Ketones are reduced to the corresponding alcohols by (i)addition of H2 in

presence of catalyst (Catalytic hydrogenation),such as finely divided Pt, Pd, Ni, or

Ru,(ii) By nascent hydrogen obtained by the action of Na/C2H5OH and (iii)By complex

metal Hydrides such as LiAlH4 or NaBH4.

Catalysts : H2/Ni or Na/C2H5OH or LiAlH4 or NaBH4

Catalyst

HCHO → CH3OH Catalyst R-CHO → R-CH2-OH pri alcohol

(7) Action of Grignard reagents: All the three types of the alcohols can be

prepared by this method. An aldehyde or Ketone undergoes nucleophilic addition of

Grignard reagent in presence of dry ether to form a complex which on acid hydrolysis

gives an alcohol. It occurs in two steps

Step I : Nucleophilic addition of Grignard reagent to the carbonyl group to form an

adduct

Step II : hydrolysis of adduct to yield alcohol

(I)Primary alcohol is produced with methane (ii)Secondary alcohol is obtained with other aldehydes

(III)Tertiary alcohol is produced with ketones

9 | P a g e

(8)Reduction of carbonyl group including carboxylic acid and esters:

Reduction of carboxylic acids with LiAlH4 or better with B2H6 gives primary alcohols.

Diborane, however, does not easily reduce functional groups such as ester, nitro

halo,etc.thus

LiAlH4 Or B2H6/ether

R-COOH → R-CH2-OH LiAlH4

RCOCl → R-CH2-OH + HCl Acetyl chloride primary alcohols LiAlH4 R(CO)2O → 2R-CH2-OH Acid anhydride

4

Reduction of carboxyl compounds and esters to alcohol by using alcoholic sodium

is called Bouveault – Blance reduction.

O Na/alcohol CH3-C-OC2H5 → 2CH3CH2OH Ethyl alcohol

(9)From epoxides :

Epoxyalkanes such as oxiranes or Ethylene oxide react with Grignard reagent in the

presence of anhydrous ether to form addition products which are hydrolysed by water in

the presence of acid to form alcohols and on reduction in the presence of LiAlH4 gives

Alcohols. (i)Reduction (ii)Action of Grignard reagent RMgX + CH2-CH2 → RCH2-CH2-OMgX O

R-CH2-CH2-OH +Mg(OH)X

(10)Oxo process : This reaction is also known as carbonylation or hydroformylation reaction

2CH2-CH=CH2+2CO+2H2 → CH3CH2CH2-CHO

Cu-Zn(H2) or LiAlH4

CH3CH2CH2-CHO → CH3CH2CH2CH2OH

10 | P a g e

(11)Fermentation of carbohydrates:

Ethanol or ethyl alcohol or grain alcohol can be prepared on commercial scale by the

fermentation of sugar (present in molasses and grapes etc) or starch (present in Rice,

berlay, maize etc).The reactions that are taking place are catalysed by certain enzymes

also called Biocatalysts.

(i)From Molasses

Molasses is the mother liquor after crystallization of sugar from sugar solution Invertase

C12H22O11 + H2O → C6H12O6 + C6H12O6 Glucose fructose

Zymase

C6H12O6 → 2C2H5OH + CO2 Ethyl alcohol

(ii)From starch Diatase Maltase

2(C6H10O5)n +nH2O → nC11H22O11 → 2nC6H12O6 H2O

Zymase

C6H12O6 → 2C2H5OH +CO2

(12) Reduction of water gas

It is an industrial method for preparation of methanol

PHYSICAL PROPERTIES OF ALCOHOLS

(i) Physical state

*At ordinary temperature, lower members upto C11 are colourless liquids. Higher

members are wax like solids The lower members have a characteristic smell and a

burning taste while higher members are almost colourless ,odourless waxy solids.

*Alcohol are lighter than water

11 | P a g e

(iii) Boiling point

*Boiling points of alcohols are much higher than corresponding aliphatic hydrocarbons

and halo alkanes.

*Among isomeric alcohol, the boiling points decrease in the following

order Primary > Secondary > tertiary

*The boiling point decreases with branching.

*The high boiling points of alcohol are mainly due to the presence of intermolecular

hydrogen bonding in them which is lacking in ether and hydrocarbons.

(iv) Solubility

*Alcohols can form hydrogen bonds with water and break H-bond between water

molecule.

*Lower alcohols are soluble in water due to hydrogen bonding but solubility

decreases with increase of molecular mass since hydrocarbon part increases which

interrupts the hydrogen bond formation.

*Solubility increases with branching since surface area of hydrocarbon part

decreases with increase of branching.

CHEMICAL PROPERTIES OF ALCOHOLS

Alcohols are versatile compounds. They react both as nucleophile and electrophile

*Alcohol as nucleophile *Alcohol as electrophile

12 | P a g e

Chemical reactions of alcohols can be classified into following categories

(A) Reactions due to O-H bond, breaking

(B) Reactions due to C-OH bond breaking

(C) Reaction of alcohol molecule as a whole

(A)Reactions due to O-H bond, breaking Order of ease of cleavage of O-H bond and thus order of reactivity is CH3OH > primary > secondary> tertiary

1. Reaction with metals ( acidic nature):

2R – O – H + 2Na → 2R-O-Na +H2

Sodium alkoxide

Alcohols are stronger acid than acetylenes and acidic nature is in the order H-OH > ROH> CH≡CH > NH3RH

Acidic character of alcohol and water

*Alcohols act as Bronsted acids which lose a proton to strong base *Electron releasing inductive effect (+I) of the alkyl group makes the alcohol weaker acids than water. *On treating alkoxide ion with water, the starting alcohol is obtained

.

Comparison of acidic character of primary, secondary and tertiary alcohols The acidic

character of alcohols is due to the polar nature of O – H bond an electron releasing

group increases electron density on oxygen tending to decrease the polarity of O – H

bond. This decreases the acidic strength and so the acid strength of alcohol decreases in

13 | P a g e

the following order

RCH2OH > R2CHOH > R3COH Order of +I effect in various isomeric alcohols is

CH3OH < Primary < secondary < tertiary

2. Esterification : *If the above reaction is carried out with dry HCl gas as catalyst, the reaction is known

as Fischer-Spcier esterification

*Order of reactivity of different alcohols towards esterification is

CH3OH > RCH2OH > R2CHOH > R3COH

*As the size of hydrocarbon part (R) around –OH increases, rate of reaction

decreases due to steric hinderance

3. Reaction with inorganic acid

C2H5OH + HOSO2OH → C2H5SO3OH + H2O H2O

Sulphuric acid ethyl hydrogen sulphate

C2H5OH + HO-NO2 → C2H5-O-NO2 + H2O

Nitric acid ethyl nitrate

4. Acylation or reaction with acid chloride and acid anhydrides

*When alcohols reacts with acid chloride or acid anhydrides, the hydrogen of the

hydroxyl group is replaced by an acyl group (RCO-) resulting in the formation of

esters. The process is known as acylation

*When the hydrogen of –OH group is replaced by CH3CO- (acetyl) group, the process

is termed acetylation.

*The acetylation of alcohol is usually carried out in the presence of base such as pyrimidine.

14 | P a g e

(B) Reaction due to C – OH bond breaking

Order of ease of cleavage of C – OH bond and thus reactivity of different alcohols is Tertiary > Secondary > Primary > CH3OH

1. Reaction with halogen acids

R – OH + H – X → R-X +H2O

*For a given hydrogen halide order of reactivity of different alcohol is

*Allyl > benzyl > 3o > 2

o > 1

o

*Order of reactivity of HX is

HI > HBr > HCl

(i)With HCl-

Due to low reactivity, the reactions of primary and secondary alcohols with HCl require

the use of some Lewis acid catalyst such as anhydrous zinc chloride. However, tertiary

alcohol react readily with conc. HCl even in the absence of a catalyst, i.e., anhydrous

ZnCl2.

Anhydrous ZnCl2 CH3CH2-OH + H-Cl → CH3CH2-Cl +H2O ∆ 1-chloro ethane

CH3 CH3 Anhydrous ZnCl2 HC-OH + H-Cl → HC-Cl +H2O

CH3 CH3 2-chloroPropane

CH3 CH3 Anhydrous ZnCl2 CH3-C-OH + H-Cl → CH3- C-Cl + H2O

CH3 CH3 2-chloro-2-methylPropane

15 | P a g e

(ii)With HBr-

Like HCl, the reaction of primary alcohols with constant boiling HBr (48%) is

carried out in presence of a small amount of conc. H2SO4 as catalyst. No catalyst is

required for secondary and tertiary alcohols because they undergo dehydration in

presence of conc. H2SO4 to give alkenes

Cocn.H2SO4

CH3-CH2-OH + HBr → CH3CH2-Br + H2O reflux

(iii)With HI-Alkyl halides are formed, on refluxing alcohols with constant boiling HI (57%). Reflux

CH3OH + HI → CH3-I + H2O

However, when an alcohol is heated with HI in presence of red phosphorus, reduction

occurs to form the corresponding alkane.

Red P

CH3OH + 2HI → CH4 + H2O + I2 423K

2. Reaction with phosphorus halides and Thionyl chloride

Alcohols react with Thionyl chloride in presence of pyridine to form chloroalkanes or

alkyl chloride. Phosphorus halides such as PCl5, PCl3, PBr3 (P+Br2) and PI3(P+I2) react

with alcohols to form the corresponding haloalkanes or alkyl halides

R - OH + PCl5 → R-Cl + POCl3 + HCl

Chloro Phosphorus

alkane Oxychloride

3R - OH + PCl3 → 3R-Cl + H3PO3

Chloro Phosphorus

alkane acid

3R - OH + PBr3 → 3R-Br + H3PO3

Bromo

alkane

R - OH + SOCl2 → R-Cl + SO2↑ + HCl

16 | P a g e

3. Reaction of Nitric acid

When a mixture of the vapours of an alcohol and ammonia are passed over heated

alumina (Al2O3) at 633K, A mixture of Primary, secondary, and tertiary amine is

produced.

ROH +HONO2 →R-O-NO2 +H2O Alkyl nitrite Al2o3

ROH + NH3 → RNH2 + H2O 10Amine Al2o3

ROH + RNH2 → R2NH + H2O 20Amine

Al2o3

ROH + R2NH → R3N + H2O

30 Amine

Al2o3

ROH + R3N → (R4N+)OH- (R4N+)OH-: Quaternary alkyl ammonium hydroxide

(C) Reaction involving alcohol molecule as a whole

1. Dehydration

Dehydration (removal of a molecule of water)of alcohols can lead to the formation of either

alkenes or ethers.This dehydration can be carried out either with protonic acids such as conc.

H2SO4,H3PO3 or catalysts such as anhydrous zinc chloride or alumina.

(a)With protonic acids

Mechanism of dehydration Step I: Formation of protonated alcohol

Step II : Formation of carbocation. It is the slowest step and hence the rate determining step of the reaction

17 | P a g e

Step III : Formation of ethene by elimination of proton

* Formation of 2-methyl but-2-ene

Mechanism In case of secondary and tertiary alcohols, Saytzeff’s rule is followed and the ease of dehydration of alcohol is in the order Tertiary > Secondary > Primary

(b) with heated Alumina (Al2O3):When vapours of an alcohol are passed over heated

alumina, different products are obtained at different temperature as given below.

(i) At 513- 523K , intermolecular dehydration takes place to form ethers

Al2O3

2C2H5OH → CH3CH2-O-CH2CH3 + H2O

513-523K

(ii) At 633K, intramolecular dehydration takes place to form Alkenes

Al2O3

C2H5OH → CH2=CH2 + H2O

623K

2. Dehydrohalogenation (a)A primary alcohol loses hydrogen and forms aldehyde Cu/573k

RCH2OH → RCHO + H2 (b) A secondary alcohol loses hydrogen and form a ketone

18 | P a g e

Cu/573k R2CHOH → ( R )2C=O + H2 (c)A tertiary alcohol undergoes dehydration of alkene Cu/573k

(CH3)3COH → (CH3)2C=CH2 + H2

3. Oxidation (i) Primary alcohols on oxidation gives aldehydes which further get

oxidized to carboxylic acid

Oxidation can be stopped at aldehyde stage by using collin’s reagent

( CrO3∙2C5H5N, chloroform trioxide-pyridine complex) or pyridinium chlorochromate,

PCC ( CrO3 ∙ 2C5H5N∙HCl )

(ii) Secondary alcohols on oxidation give mixture of carboxylic acids

This oxidation can be stopped at ketone stage by using (CrO3)

(iii) A tertiary alcohol having no oxidisable hydrogen linked to carbon atom bearing

hydroxyl group, is stable to oxidation in neutral or alkaline KMnO4 solution

19 | P a g e

4. Reaction with bleaching powder:

Chloroform was discovered by Libig in 1831 and named was given to Dumas. It can be

prepared by the action of aqueous paste of CaOCl (bleaching powder/Calcium

oxychloride) with ethanol. After completion of reaction chloroform distilled at 334 K and

it is dried over fused CaCl2.

Hydrolysis

CaOCl2 + H2O → Ca(OH)2 + Cl2 Oxidation CH3CH2OH + Cl2 → CH3CHO + 2HCl

Chlorination 2CH3CHO + 3Cl2 → CCl3CHO + 3HCl

Hydrolysis 2CCl3CHO + 3Ca(OH)2→ 2CHCl3 + (HCOO)2Ca

5. Haloform Reaction Compound having at least one methyl group linked to the carbonyl carbon atom i.e., these

compounds are easily oxidized by sodium hypohalite solution (Cl2,Br2,I2 in the presence of dil

NaOH) to give Haloform (Chloroform, Bromoform or Iodoform ).

When the reaction is carried out with sodium hypoiodite NaOI (I2 +aq. NaOH), a yellow ppt. of

iodoform is produced.

heat

CH3CH2OH + 4I2 + 6 NaOH → CHI3 + 5NaI + HCOONa + 5H2O Sodium Formate

This reaction like the preparation of chloroform also in three steps

Oxidation Iodination hydrolysis

C2H5OH → CH3CHO → CI3CHO → CHI3

(NaOH+I2) (NaOH) I2

CH3CHO + 3I2 → CI3CHO + 3HI Acetaldehyde

CI3CHO + NaOH → CHI3 + HCOONa Iodoform

(yellow ppt)

CH3COCH3 + I2 → CI3COCH3 + 3HI

CI3COCH3 + NaOH → CHI3 + CH3COONa Acetone

place of iodine, bromine or chlorine can be taken when the corresponding compounds

bromoform or chloroform are to be formed. This reaction in general is known as

haloform reaction.

20 | P a g e

SOME COMMERCIALLY IMPORTANT ALCOHOLS

1. Methanol (Wood Spirit or Wood naphtha) *for the manufacture of formaldehyde which is widely used as a preservative for

biological specimens and in the manufacture of formaldehyde resins such as Bakelite,

melamine-formaldehyde, urea-formaldehyde, etc.

* for denaturing ethyl alcohol i.e., to make it unfit for drinking purposes, Denatured

alcohol is commonly known as methylated spirit.

*In the manufacture of perfumes, drugs and varnishes.

* as an antifreeze for automobile radiators.

* It is used as solvent in paints, varnishes and celluloid.

2. Ethanol (Spirit of Wine or Grain alcohol) *Ethanol is produced by fermentation of molasses into glucose and Fermentation gives ethanol and carbon dioxide

Invertase

C12H22O11 + H2O → C6H12O6 + C6H12O6 Glucose fructose Zymase

C6H12O6 → 2C2H5OH + CO2

* It is used as solvent for dyes, oils, perfumes, varnishes, gums, paints cosmetics etc. * It is used as solid alcohol fuel. It is prepared by mixing ethanol with saturated calcium acetate solution. A solid gel is formed is known as canned heat or solid alcohol. It burn like alcohol.

* The commercial alcohol is made unfit for drinking by mixing in it some copper

sulphate ( to give color) and pyridine ( afoul smelling liquid). It is known as

denaturation of alcohol.

* It is used as antifreeze in automobile radiator, antiseptic, Petrol substitute (Power

alcohol).

* It is used in Thermometer, Spirit lamp, explosive etc.

21 | P a g e

* Phenol are the aromatic hydroxy compounds in which one or more

hydroxyl (-OH) groups are directly attached to benzene ring. If –OH group is not directly

attached to benzene ring it is called aromatic alcohol.

* Simple phenol is hydroxy benzene or phenyl hydroxide or benzenol

or phenol itself also known as carbolic acid. It is represented as Ar-OH Or Ph-OH where

Ar or Ph is C6H5-group.

CLASSIFICATION OF PHENOL

Phenols are classified as mono, di and trihydric phenols according to the number

of hydroxyl groups attached to the aromatic ring.

1. Monohydric phenols

2.Dihydric phenols

3. Trihydric phenols

22 | P a g e

ELECTRONIC STRUCTURE OF PHENOL

* The O-H bond in phenol , like the O-H bond in alcohols, is formed by overlap of a sp3-

orbital of oxygen with 1s-orbital of hydrogen while the C-O bond is formed by the

overlap of a sp3-orbital of oxygen with a sp2-orbital of carbon of the benzene ring .

* The C-O-H bond angle in phenol is approx the same (1090) as in methanol but the

carbon-oxygen bond length in phenol is, however, slightly less (136pm) than methanol

(412pm).

* This is due to (i) resonance as a result of which carbon-oxygen bond acquires some

double bond character because of conjugation of the lone pair of electrons of oxygen with

the benzene ring and (ii) sp2-hybridised state of carbon to which oxygen in attached.

* Phenol has dipole moment 1.54D where as methanol has dipole moment 1.71D. This

smaller dipole moment of phenol is due to the electron attracting effect of phenyl group

in contrast to the electron releasing effect of methyl (or alkyl) group in alcohol

GENERAL METHODS OF PREPARATION OF PHENOLS

INDUSTRIAL METHOD

1. Middle oil fraction of coal tar distillation:

On reaction with aq. NaOH phenols are dissolved in it as phenoxide, CO2 is then blown

through this phenoxide ion solution to liberate phenols

Fractional washed

Coaltar → Middle oil (1700-2300) → Middle oil fraction-basic impurities (like pyridine) Distillation H2SO4

Excessive aq NaOH CO2/H2O

→ Middle oil fraction-Naphthalene separate → C6H5ONa → Phenol-(crude) + Na2CO3 Cooling ↓fractional distillation Phenol-1800

Cresol-1900-2050

Xylols-2110-2350

On reaction with aq.NaOH phenols are dissolved in it as phenoxide, CO2 is then blown through

this phenoxide ion solution to liberate Phenols.

23 | P a g e

2. Hydrolysis of aryl halides (Dow’s process):

In this method, chlorobenzene is heated with excess of aqueous sodium hydroxide (6-8%)

at 623K under pressure of 320 atm. Sodium phenoxide formed in the process is

hydrolyzed.

using dilute hydrochloric acid to get phenol. Alternatively a current of carbon dioxide is

passed through aqueous sodium phenoxide to get phenol.

However if some electron withdrawing group is attached to benzene ring, then reaction

conditions get relaxed.

24 | P a g e

3. Oxidation of iso-propyl benzene (Cumene) :

Cumene (isopropylbenzene or 2-Propyl benzene or 2-Phenyl propene) is prepared

by friedel craft alkylation of benzene with propene or propyl chloride in presence of

phosphoric acid or AlCl3.This on aerial oxidation forms cumene hydroperoxide which

upon subsequent hydrolysis with an aq. acid gives phenol and propanone

This reaction is also called Auto-oxidation

4. From Chlorobenzene Rasching’s process:

When chlorobenzene is heated with steam at 500K in presence of Ca3(PO4)2 or SiO2 or

CuCl2 gives phenol. This method is more economical than Dow’s method since, HCl

produced can be reused in the preparation of Chlorobenzene from benzene. A mixture of

benzene vapours, air and hydrogen chloride is passed over heated CuCl2 at 500K.

25 | P a g e

LABORATORY METHOD

1. From benzene sulphonic acid:

Preparation of Phenol from benzene sulphonic acid involes three steps.

1) Step-I Neutralisation

Benzene sulphonic acid is neutralized by aq. alkali like NaOH. It forms sodium salt of

benzene sulphonic acid or sodium benzene sulphonate.

2) Step-II Fusion:

Sodium benzene sulphonate salt is fused with solid caustic soda at 573K to 623K. It gives

sodium phenoxide (sodium phenate) .

3) Step-III Acidification

Sodium phenoxide is then acidified with dil HCl/dil. H2O+CO2 mixture i.e. (Carbonic

acid) to get phenol.

The above reaction is laboratory method for preparation of phenol.

2. Hydrolysis of diazonium salt:

(I) Benzene,on nitration gives Nitro benzene.

(II) On reduction of nitrobenzene in presence of Sn/HCl giveS Aniline.

(III) When Aniline is reacted with nitrous acid (NaNO2+HCl) at 273K to 278k gives

benzene diazonium chloride.

26 | P a g e

(IV) By acid hydrolysis to get Phenol.

3. Decarboxylation of salicylic acid:

Phenol is obtained by decarboxylation of sodium salt of salicyclic acid with soda lime

(CaO+NaOH) followed by acidification with dilute HCl.

4. Oxidation of Grignard reagent:

When oxygen is bubbled through an ethereal solution of phenyl magnesium bromide it

forms an addition product which upon treatment with a dilute mineral acid gives phenol.

27 | P a g e

5. Oxidation of aromatic hydrocarbons:

On Oxidation ,Toluene gives phenol in presence of cupric salt as a acatalyst.

PHYSICAL PROPERTIES OF PHENOL

1.Physical state *At ordinary temp. lower alcohols are colourless liquids with distinct smell and burning taste. The higher members are colourless, odourless waxy solids. but they reddish brown due to auto oxidation on exposure to air and light. *Phenols are poisonous in nature but act as disinfectant and antiseptic.

2.Solubility *Phenols form H-Bonds with water molecule and hence soluble in water, but their

solubility is lower than that of alcohols because of large hydrocarbon part .Phenols, like

alcohols,also form intermolecular hydrogen bonds

*Phenols, like alcohols, exist as associated molecules.

3.Boiling point *Phenols have much higher boiling point than there corresponding hydrocarbons due to intermolecular hydrogen bonding. *Amongst the isomeric nitrophenols, o-nitrophenol is steam volatile due to

chelation (intramolecular H-bonding) while p-isomer is not steam volatile due to

association of molecules by intermolecular H-bonding. Further, due to chelation,

o-nitrophenol has lower m.p. and b.p. lower acidity and lower solubility in water

than p-nitrophenol.

28 | P a g e

On the other hand meta and para nitrophenol exhibit intermolecular H-bonding with their

own molecules as well as with water molecules and hence show comparatively higher

melting and solubility. (i) Intermolecular H-bonding (m –nitrophenol)

(ii) H- bonding with water molecules ( m-nitrophenol)

(iii) Intermolecular H- bonding ( p –nitrophenol)

(iv) H – bonding with water molecules ( p – nitrophenol)

CHEMCIAL PROPERTIES OF PHENOL

(A)Reactions involving cleavage of O- H bond

1. Acidic character of phenol (i) Reaction with active metals: Phenols are weak acidic in nature. they can react with active alkali metals (NaOH, KOH) to form salts known as phenoxides or phenates.

29 | P a g e

(ii)Reaction with alkalies

*They do not react with carbonates and bicarbonates. Phenols are weaker acid as

compared to carboxylic acid because of polar O-H group in them. The acidic nature

of phenol is due to formation of stable phenoxide ion in solution to give H+.

Comparison of acidic character of alcohols and water

Alohol behave as Bronsted acids, i.e. they can donate a proton to a strong base (:B-).

.. -.. B :

- + H-O-R → B-H + : O-R

.. .. Base Alcohol(acid) (conjugated acid) Alkoxide ion(conjugated base)

However, when an alkoxide ion reacts with water, the starting alcohol is obtained. -.. .. .. -.. R-O: + H-O-H → H-O-R + :OH .. .. .. .. Base Acid (conjugated acid) (conjugated base)

This reaction suggests that water is a better proton - donar than alcohol. alcohols are

weaker acids than water. Conversely, alkoxide ion is a better proton acceptor than

hydroxide ion.i.e. alkoxides are stronger bases than hydroxide ion.

Explanation for stronger acidic character of phenols than alcohols

*phenols are stronger acid than alcohols

i.)The greater acidity of phenol is due to stability of phenoxide ion is resonance

stabilized.

ii.) Resonance structure of phenol

30 | P a g e

iii.) As a result of resonance, the oxygen atom acquires a partial charge. this weakens the

O-H bond and thus facilities the release of a proton. thus, facilities the release of a proton.

Thus, phenols like alcohols also act as Bronsted acids facilitates the release of proton

(H+) to give phenoxide ion which is also stable due to resonance

iv.) Resonating structure of phenoxide ion .

v.) Both phenol and phenoxide ion are stabilized by resonance. But phenoxide ion is

more stabilized than phenol because the resonating structure of phenoxide ion carry

only negative charge of phenol involves separation of positive and negative charge.

Hence, phenol has a strong tendency to form more stable phenoxide ion by releasing

a proton.In contrast, neither the alcohol nor the alkoxide ion is stabilized by

resonance.

Effect of substituent on the acidity of phenols

a.Electron withdrawing group (EWG)

*Electron withdrawing groups NO2 , -X, -CHO, -COOH, -CN etc. stabilizes the

phenoxide ion more by dispersing the negative charge relative to phenols ( i.e. proton

release become easy) and thus increases the acidic strength of phenols

Particular effect is more when the substituent is present on o– and p-positions than

in m- position. Thus acidic strength of nitrophenol decreases in the order p-nitrophenol > o-nitrophenol > m-nitrophenol > phenol

*Further greater the number of electron withdrawing groups at o- and p – position,

more acidic the phenol.

b.Electron donating group (EDG)

(i) Electron donating group –R, -NH2, -OR etc destabilize the phenoxide ion by donating

electrons and intensify the negative charge relative to phenol (i.e. proton release become

difficult)and thus decreases the acidic strength of phenol.

31 | P a g e

(ii)The effect is more when the substituent is present on o- and p-position than on m-

position with respect to –OH group. Thus cresol are less acidic than phenol.

m – methoxy and m-amnion phenols are stronger acid than phenols because of –I

effect ( of –OCH3 and –NH2 groups) and absence of +R effect. m –methoxy phenol > m-amino phenol > phenol > O-methoxy phenol > p-methoxy phenol

2.Ester formation :

Phenols also react with acid chloride and anhydrides to give esters in excellent yields.

The reaction with acetyl chloride is usually catalysed by a base such as pyridine, that

with acetic anhydride is catalysed both by acids (a few drops of conc. H2SO4) and bases

(sodium acetate, pyridine).

Reaction with benzoyl chloride is known as benzoylation

Benzoylation of alcohols o phenols in presence of NaOH is called Schotten-

Baumann reaction

32 | P a g e

3.Ether formation: Phenol react with alkyl halide in presence of NaOH give alkoxy benzene. NaOH

C6H5OH + CH3CH2Br → C6H5OCH3CH2 + NaBr + H2O Ethoxy benzene

4.Claisen Rearrangment of Aryl Allyl Ethers

Reaction type : Electrocyclic reaction or sigmatropic rearrangement

*Aryl allyl ethers undergo a thermal rearrangement to give ortho-allyl phenols.

*This reaction is an intramolecular process.

*A sigmatropic rearangement is a reaction is which a σ bond migrates from one end of a

π system to the other.

(B) Electrophilic aromatic substitution reaction The hydroxyl group is a powerful activating group and hence phenols readily undergo

electrophilic substitution reactions. In this reaction, an electrophile (electron loving species)

attacks the benzene ring and replaces one of its hydrogen atoms. Since the ortho and

para positions of the phenol are electron rich, the substitution takes place at these positions.

Two such reactions are halogenation and nitration reactions. Let us now study them in

details.

33 | P a g e

1. Halogenation

Phenol reacts with bromine in aqueous solution to give 2, 4,6- tribromophenol in

about 100% yield. Bromination can be limited to mono bromination to give mainly 4-

bromophenol using low temperature and less polar solvent such as carbon disulphide. The

other product formed in minor quantity is 2-bromophenol.

Due to steric hinderance at ortho position, para-product predominates

2. Sulphonation :

34 | P a g e

3. Nitration:

Phenol gives a mixture of 2-nitro and 4-nitrophenols on nitration with dilute nitric acid.The

mixture of nitrophenols so obtained is separated using steam distillation. Both these

products show hydrogen bonding. In case of 2-nitrophenol, the hydrogen bonding is

intramolecular (in the same molecule) whereas in case of 4-nitrophenol, it is

intermolecular (between different molecules). Nitrophenol is steam volatile and distills

out on passing steam whereas 4-nitrophenol is less volatile due to intermolecular hydrogen

bonding.

Treatment of phenol with a mixture of conc. nitric acid and conc. sulphuric acid at 323K

yields 2,4,6-trinitrophenol also known as picric acid.

4. Mercuration

35 | P a g e

4. Friedel crafts alkylation and acylation Phenol reacts with alkyl halides in presence of anhydrous AlCl3 to form para product with a small quantity of ortho isomers

6.Nitrosation

Phenol is treated with Nitrous acid (NaNO2+HCl) and nitrosophenol thus obtained

is oxidized with dil. HNO3, the yield of mononitrophenol is increased.

36 | P a g e

7. Kolbe’s reaction: involves sodium phenoxide which is allowed to absorb carbon dioxide and then

heated under a pressure of CO to 398 K. Sodium salicylate so obtained on

acidification yields

Mechanism

37 | P a g e

Acetyl salicylic acid ( Aspirin) (2-acetoxy benzoic acid) Salicylic acid is the starting material for the manufacture of 2-acetoxybenzoic acid

.It is obtained by acetylating salicylic acid with acetic anhydride (Sodiumacetate or

acetic acid) and few drops of conc.H2SO4.

It is a white solid (m.pt. 408K) and is used for relieving pain (analgesic) and to bring down the body temperature (antipyretic during fever)

(b) Methyl salicylate

It is prepared by refluxing salicylic acid with methyl alcohol

*It is an oily liquid (b.pt. 495K) with pleasant odour (oil of wintergreen) used in

perfumery and flavorings agent.

*It is also used in medicine in the treatment of rheumatic pain and as a remedy

for aches, sprains and bruises.

38 | P a g e

(c) Phenyl salicylate ( salol)

It may be prepared by heating salicylic acid with phenol in the presence of

phosphoryl chloride.

It is white solid (m.pt 316K) and is used as an intestinal antispeptic.

8. Reimer-Tiemann reaction: When phenol is refluxed with chloroform in the presence of aqueous sodium

hydroxide at 340K followed by hydrolysis,an aldehyde group (-CHO) gets

introduced in the ring at apposition ortho to the phenolic group. Ortho hydroxyl

benzaldehyde or Salicyldehyde is formed as the product of the reaction.

This reaction is called Reimer-Tiemann reaction.In addition to O-salicyldehyde,

small amount of p-salicyldehyde is also formed but the major product is ortho.

Mechanism The electrophile, dichloromethylene CCl2 is generated from chloroform by action of base

OH- + CHCl3 ⇆ HOH + CCl3 → Cl- +:CCl2

39 | P a g e

Attack of electrophile ( :CCl2) on phenoxide ion

Salicylaldehyde If the reaction is carried out with carbon tetrachloride (CCl4) instead of chloroform, o -hydroxy benzoic acid (salicylic acid) is formed.

TESTS TO DISTINGUISH BETWEEN ALCOHOLS AND PHENOLS

1. Litmus test Phenol turns blue litmus red being acidic in nature but alcohol do not.

They turn blue litmus paper red. Acidity of phenol is due to the formation of H+ ion

and stable phenoxide ion in the solution.

C6H5OH + 2Na → 2C6H5ONa + H2↑

C6H5OH + NaOH → C6H5ONa + H2O 2. Ferric chloride test Phenol react with neutral ferric chloride solution to form violet or green colored solution (water soluble complex compounds) where as alcohol do not undergo such reactions.

40 | P a g e

3C6H5OH + FeCl3 → (C6H5O)3Fe + 3HCl

(C6H5O)3 Fe : Ferric phenoxide ( violet complex)

In fact, all compound containing enolic group (=C-OH) give this test.

3. Bromine water test Aqueous solution of phenol forms white precipitate of 2,4,6-tribromo phenol,

when treated with bromine water. However alcohol so not give such

precipitation.

USES

* Dilute solution of Phenol is used as antiseptic and disinfectant.

* Phenol is used in preparation of salicylic acid, Aspirin (analgesic), phenacetin ,

paracetamol (antipyretics) and dyes (Phenolphthalein)

* Phenol is used in preparation of explosive such as picric acid.

* It is used as preservative for wood and ink.

* It is used to prepare 2, 4- dinitro phenoxy ethanoic acid which is selective weed

killer.

* It is used in preparation of adhesive i.e. Bakelite resin (phenol formaldehyde

resin), epoxy resin, ion exchange resin.

41 | P a g e

Ethers are organic compounds containing divalent oxygen atom attached to two

same or different alkyl groups. In ether divalent oxygen atom (-O-) is a

functional group.

Ethers have a general formula R - O - R’, where R and R’ may be same or

different alkyl or aryl or arylalkyl groups.

*Ethers can be classified as follows: (I)Aliphatic ethers If both R and R’ groups are alkyl groups, then ether is aliphatic ether

CH3 – O – CH2CH3 (ethyl methyl ether) CH3CH2 – O – CH2CH3 (diethyl ether)

(II)Aromatic ether If both R and R’ or any of them is aryl group then ether is aromatic ether

CH3– O –C6H5 ( methyl phenyl ether)

C6H5 – O – C6H5 (Diphenyl ether)

Depending upon the nature of alkyl group s attached to oxygen, ethers are two types

(III)Simple or symmetrical ether If two group R and R’ present in ether are same, then it is known as simple or symmetric ether

CH3 – O – CH3 (Dimethyl ether)

C2H5 – O – C2H5 (Diethyl ether)

C6H5 – O – C6H5 (Diphenyl ether)

(IV)Mixed or unsymmetrical ether If R and R’ present in ether are different, then ether is known as mixed or unsymmetrical ether

CH3 –O – C2H5 (ethyl methyl ether)

CH3–O-C6H5 (methyl phenyl ether) C6H5 – O – CH2C6H5 (Benzyl phenyl ether)

Isomerism in Ethers

1.Functional Isomerism:

both –O- and –OH are the functional groups.

42 | P a g e

Ethers are isomeric with mono-hydric alcohol eg.-C2H6O

CH3CH2OH ( ethyl alcohol)

CH3 – O –CH3 ( dimethyl ether)

2.Metamerism: Ethers containing more than three carban atoms shows such type of isomerism. CH3-CH2-CH2-O-CH3 C2H5-O-C2H5 Methyl n-propyl ether Diethyl Ether

3.Chain isomerism

It is due to difference in the nature of carbon chain. CH3-O-CH2-CH2-CH2-CH3 CH3-O-CH2-CH-CH3 CH3 n-butyl methyl ether Isobutyl methyl ether

STRUCTURE

Ether may be considered as dialkyl derivative of water. In ether , oxygen atom

undergoes sp3 hybridization.It has structure similar to that of water. oxygen atom has

four sp3 hybrid orbitals out of four, two sp3 hybrid orbitals form two sigma bond with

two alkyl groups by sp3-sp3 overlapping. Remaining two sp3 hybrid orbitals contains

lone pair of electrons. It has bent or angular structure C-O-C bond angle in ether is

1100 which is greater than water, This is because in ethers alkyl groups have repulsive

forces among themselves but in water. This repulsion between the H-atom is absent.

thus ether possess net dipole moment.

ETHERS

43 | P a g e

GENERAL METHOD OF PREPARATION OF ETHERS

1. Dehydration of alcohols

(i) Acidic dehydration of alcohols

This method is used to prepare simple or symmetrical ether. In this reaction, reaction

conditions have to be carefully controlled, to get the maximum yield of ether. At a

slightly higher temperature (150oC) alkene is obtained instead of ether.

Mechanism

SN1 mechanism

SN2 mechanism

Primary alcohols reacts by generally SN2 mechanism where as secondary and tertiary alcohols undergo the reaction by SN1 mechanism Order of ease of dehydration of alcohol to form ethers 1O alcohol > 2O alcohol >3O alcohol (ii)Catalytic dehydration

(Al2O39523K)

2R-OH → R-O-R + H2O

44 | P a g e

2.Williamson synthesis When Sodium alkoxide is heated with alkyl halide in alcohol, ethers are obtained . This

method is called Williamsons synthesis. It is laboratory preparation method of ethers.

R’ – ONa + X – R → R’ – O – R + NaX

Both symmetric and unsymmetrical ethers can be prepared by this method Mechanism Symmetric or simple ether

C2H5ONa ⇌ C2H5O- + Na+

Unsymmetric or Mixed ether CH3-O-Na + Br-C2H5 → CH3-O-C2H5 + NaBr

Order of reactivity of alkyl halides towards this reaction is Primary > secondary > tertiary For better yield, the alkyl halide should be primary and alkoxide should be secondary or tertiary

3. Action of silver oxide on alkyl halide heat

2RX + Ag2O → R-O-R + 2Ag

4. Action of diazomethane on alcohols

When Diazomethane is reacted with alcohol in presence of fluoroboric acid or BF3 it gives

methyl ethers. HBF4

CH3-CH2-OH + CH2N2 → CH3-CH2-OCH3 + N2 Diazomethane ethyl methyl ether (mixed ether)

5. Reaction of lower halogenated ether with Grignard reagent

45 | P a g e

6. Addition of alcohols to alkene

By direct addition of alcohols to reactive alkenes in presence of acids as catalyst.

Mechanism H2SO4 → H+ + H2SO4

-

PHYSICAL PROPERTIES OF ETHERS

* dimethyl ether and ethyl ether are gases while All ethers are colourless liquids at

room temperature

* Ethers are sparingly soluble in water but readily soluble in organic solvent like alcohol,

chloroform, Benzene etc.

*The solubility of lower ethers in water is due to formation of hydrogen bonding with

water but tendency to form hydrogen bonding decrease in number of alkyl groups.

Hence ethers are not soluble in water.

* Ethers are lighter than water and they form upper layer when mixed with it.

* they are highly inflammable.

* When ethers are exposed to oxygen in presence of sunlight they form explosive

hydroperoxide. * Due to the low polarity of ethers they do not form inter molecular hydrogen bonding

therefore they have low boiling points than isomeric alcohols and almost same as

alkanes of comparable molecular weight.

* Ethers are polar in nature and its dipole moment ranges from 1.15D to 1.30D

46 | P a g e

CHEMICAL PROPERTIES OF ETHERS Ethers are relatively, almost as inert compound, These are not easily attacked by alkalies,

dilute mineral acid. they are stable to catalytic hydrogenation and to other reducing

agents such as LiAlH4. this is due to the reason that the functional group of ethers(-O)

does not contain any active site in their molecules as compared to hydroxyl (-OH) group

of alcohols and phenols even though the oxygen atom atom in both these functional

groups contains two lone pairs of electrons. However, under specific conditions, ethers

undergo the following reactions.

(I)Reactions of the ethereal Oxygen

1. Action of concentrated acids(formation of oxonium salt)

The oxygen atom in ether molecule has two lone pairs of electrons, Therefore, ethers

actas Lewis bases and dissolve in cold concentrated mineral acids(H2SO4,HCl) to form

stable oxonium salts.

+ R-O-R+H2SO4(Cold) →(R- O: - R) HSO4

-

H Dialkyl Oxonium hydrogen sulphate 2.Reaction with Lewis acids: Being Lewis bases, ethers form complexes with lewis acids such as BF3, AlCl3,

FeCl3,etc.these complexes are called etherates.

CH3 CH2 .. CH3 CH2 .. O + BF3 → O BF3 CH3 CH2 .. CH3CH2 Boron trifluride etherate (complex) (II) Reaction involving the cleavage of carban – oxygen bond

1. With halogen acids:

Ethers are cleaved by strong acids HI or HBr, but HCl does not cleave ethers.This is

because, HI or HBr are sufficiently acidic to protonate ethers while iodide and bromide

ions are good nucleophiles for substitution Ethers are heated with excess of concentrated

hydrogen halide to give alkyl halides. The order of reactivity of hydrogen halides is

Reactivity of halogen acid HI > HBr > HCl

Mechanism

47 | P a g e

[During the cleavage of unsymmetrical ethers, smaller alkyl group produces alkyl halides]

(A) In cold a simple ether gives one molecule of alkyl halide and one molecule of an alcohol, while when heated gives two molecules of alkyl halide.

Cold

R-O-R + HX → R-X + R-OH ∆ R-O-R + HX → R-X + H2O (B)In cold a mixed ether gives generally a lower alkyl iodide and a higher alcohol while when heated it gives two different alkyl halides. Cold

R-O-R’ + HX → R-X + R’-OH Lower Higher ∆ R-O-R + HX → R-X + R’-X + H2O 2. With sulphuric acid:

On heating with dil. H2SO4under pressure, ethers are hydrolysed to alcohols. Dil.H2SO4. ∆

R-O-R + H2O → 2R-OH Under pressure

3. With phosphorus pentachloride:

Phosphorus pentachloride also bringsabout the cleavage of carbon-oxygen bond of ethers

leading to the formation of alkyl halides.

∆ R-O-R + PCl5 → 2R-Cl + POCl3 Alkyl chloride

4. Reaction with acid chlorides and anhydrides:

Acid chlorides react with ethers when heated in the presence of anhydrous ZnCl2 or AlCl3

to form alkyl halides and esters.

Anhydrous ZnCl2

C2H5-O-C2H5 + CH3COCl → C2H5Cl + CH3COOC2H5

48 | P a g e

(III) Reaction involving the alkyl group

1. Action of air(Formation of peroxides)

On exposure to sunlight, ethers slowly react with oxygen from air to form hydroperoxides

or peroxides which are explosive

CH3-CH2-O-CH2-CH3 + O2→ CH3-CH-O-CH2-CH3

O-O-H

1-Ethoxy ethyl hydroperoxide

2. Halogenation :

Ethers react with chlorine or bromine in the dark to give substituted products. The extent

of substitution depends upon the reaction conditions. for example, diethyl ether react with

chlorine in the dark to give α,α-dichlorodiethylether in which the halogenation

preferentially occurs at α-carbon atoms.

(IV) Electrophilic substitution reaction

The alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards

electrophilic substitution in the same way as in phenol

(i)Halogenations:

Phenylalkyl ethers undergo usual halogenation in the benzene ring, e.g., anisole

undergoes bromination with bromine in ethanoic acid even in the absence of iron (III)

bromide catalyst. It is due to the activation of benzene ring by the methoxy group. Para

isomer is obtained in 90% yield

49 | P a g e

(ii) Nitration:

Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture of

ortho and para nitroanisole.

(iii) Friedel crafts reaction :

Anisole undergoes Friedel-Crafts reaction, i.e., the alkyl and acyl groups are introduced at

ortho and para positions by reaction with alkyl halide and acyl halide in the presence of

anhydrous aluminium chloride (a Lewis acid) as catalyst

Alkylation

Acetylation

USES OF ETHER

1.It act as an industrial solvent for oils, resins, gums, etc.

2.Ethoxyethane has been used as an inhalation anaesthetic agent in surgery. however,

because of its slow effect and unpleasant recovery period, other compound such as

ethrane (or enflurane) and isoflurane (or forane) and penthrane (methoxyflurane) have

replaced ethoxyethane as an anaesthetic agent.

3.It is used as refrigerant for cooling.

4.A mixture of diethyl ether and ethyl alcohol, known as Natalite, is used as fuel.